Abstract: Excavation of foundation pit induces the horizontal displacement of soil, and the excessive horizontal displacement will cause damage to adjacent underground structures. The traditional virtual mirror technology based on the assumption of uniform convergence of circular hole underestimates the horizontal displacement of shallow soil, which is unsafe in engineering practice. Most of the research in this field is based on plane strain analysis, and the spatial effect of foundation pit cannot be considered. The two-dimensional and three-dimensional semi-analytical solutions of soil horizontal displacement considering nonuniform convergence characteristic were derived using virtual mirror technology and infinitesimal method. The nonuniform convergence mode in line with the actual situation was proposed by comparing the semi-analytical solution with the measured data, the existing theoretical solution, and the finite element results. Furthermore, the spatial effect of soil horizontal displacement was analyzed in detail based on an engineering case in Hangzhou deep soft clay. The results indicate that the limit of downward convergence is the convergence mode closer to the actual situation. The plane strain solution, which is generally considered to be safe, cannot consider the horizontal displacement of soil parallel to the retaining wall and will underestimate the total horizontal displacement of shallow soil near the corner of foundation pit. The soil displacement parallel to the retaining wall that is easily ignored in engineering practice may cause unexpected harm to shallowly buried structures such as shallow foundations and underground pipelines.

Key words: excavation of foundation pit, horizontal displacement, virtual mirror technology, nonuniform convergence, three-dimensional strain, spatial effect